Musar על סנהדרין 210:16

It may well be that this is what Rashi meant when he described the שכינה as supplying extra attributes to each of these blessings. When Rashi comments in Sanhedrin 106, that a בת קול, a "heavenly echo," added the words נטע השם in 24,6, this need not be meant literally, but refers to a prophetic insight granted Bileam by G–d at the time, which he was forced to express. Since it had been his original intention to employ the formula of blessing as a curse, the term בת קול used by Rashi is quite appropriate. Just as an echo is a follow-up to the original sound, so these words were "follow-ups" to the first part of the blessing. In the discussion of the Talmud of Bileam's blessings on folio 105, Rabbi Eleazar says that the words וישם השם דבר בפי בלעם, refers to an angel who instructed Bileam, whereas Rabbi Yonathan says that G–d put a fishhook in Bileam's mouth, i.e. He had to pronounce this prophecy whether he liked it or not.